Use Of Negative Controls Research Articles

Development of PCR-based diagnostics for soil borne plant pathogens

We believe our success with a PCR-based assay forVerticillium in plant tissue and soil samples represents a good model for other developments of this type. The universal presence of high copy ribosomal RNA genes in all organisms makes these genes especially attractive targets for gene isolation and PCR amplification. A sample dilution strategy permits the direct extraction of DNA from either soil or tissue samples without further purification, a feature which permits low cost and wide scale applications. The use of internal control templates largely eliminates the possibility of false negatives and permits quantitative analysis, something which is usually very inaccurate or impossible with traditional assays. Finally the careful preparation of PCR reagents and the use of negative controls eliminate the possibility of false positives, a careful selection of primer sequence and anneall ing conditions permits the differentiation of even closely related species. With an aim at rapid, low cost, wide scale testing a number of compromises have been included in the approaches with satisfactory results. Recent applications to nematode diagnostics appear to support the general application of our approaches to many important crop pathogens.

Early Home Environment and Mental Test Performance: A Structural Analysis

A theoretical model of early environment action was examined on a sample of 282 infants representing two racial groups (Caucasian, African-American). Children were obtained from three different sites in the United States. The model examined included the following variables: socioeconomic status (SES), early cognitive status (Bayley MDI at 12 months), stimulation within the home environment (subscales from the HOME Inventory at 12 and 24 months), parents use of negative control (subscales from the HOME Inventory at 12 and 24 months), and later cognitive status (36-month Stanford-Binet IQ). Structural Equation Modeling (SEM) with the LISREL software was used to confirm the fit of the model for African-Americans and Caucasians and for males and females separately. The models for males and females had similar structures, but not equal coefficients for all paths in the model. The models showed significant paths from socioeconomic status and early cognitive status to stimulation with the home environment, a sig...